About Flat Attack

Does this stat which is available sometimes on avatar and food buff behaves like flat weapon attack? which add automatically on attack screen for example, 1.9k total attack, we have this +100 weapon attack so it will become 2k right? or am I wrong.

 

flat attack is added to the final attack after all multipliers.
(therefore it is unaffected by any attack multipliers, except damage multipliers)

 

only on damage calculations?

 

Flat atk is added to base atk as it is, while flat weapon atk gets multiplied by atk%. So if you take same amounts of flat atk and weapon atk, weapon atk will always have greater impact on base atk.